AMHS's have been used extensively in the semiconductor fabrication field. The typical system includes a plurality of bays (rows) of storage areas. Each bay has a stocker, which includes bins for holding a plurality of containers, such as standard mechanical interface (SMIF) containers for loading 200 mm (8 inch) wafers, or front opening unified pods (FOUPs), which may be used to load 300 mm (12 inch) wafers. The stocker holds the SMIFs or FOUPs in preparation for transporting a SMIF or FOUP to the loadport of a processing tool. In technologies using larger critical dimensions (CD) and 200 mm wafers, a reticle stocker stored and delivered reticles for use in photolithographic processes. An overhead hoist transport (OHT) associated with each bay transports the SMIF or FOUP with wafers, or the pod with a reticle, from the respective stocker to a loadport for processing in one of the tools (fabrication process machines).
In conventional technologies using reticles with larger CDs, it was common to cover each reticle with a pellicle. The pellicle was a thin film of polymer secured to the reticle to prevent dirt from collecting directly on the reticle. The pellicle kept any foreign particles outside of the focal plane of the photolithographic tool used for patterning the wafer. For higher technology fabrication processes (90 nm, 65 nm and technologies with smaller critical dimensions), the pellicle material is not transparent to the extreme ultra-violet (EUV) radiation used. Because of this, higher technology reticles are often provided without a pellicle. Without the protection of the pellicle, other means are used to protect the reticle from contamination and precipitation of foreign substances.
It is known that charging (exposing) the reticle in a nitrogen (N2) atmosphere immediately before and immediately after the reticle is used for patterning a wafer will purge the reticle of impurities. The impurities diffuse out of the reticle material into the purging gas.
Thus, as shown in FIG. 1, the higher technology (smaller CD) reticles 201 were stored in a separate cabinet 202 and manually delivered by a worker 203 to an N2 charging tool 204 before and after use in the fabrication tool 205. A semiconductor fabrication facility (“fab”) may have many low volume density N2 cabinets 202 that consume significant space. These cabinets 202 were hard to manage because they were in dispersed locations. The handling procedure for reticle pod N2 charging by the operator was also complicated. This impacted the operation efficiency of the tool 205. In some instances, delay occurred when a lot 206 of wafers was ready for processing by the tool 205, but the N2 purged reticle 201 was not yet available at the tool. Errors in transferring the reticles 201 to and from the N2 cabinet 202 and failing to properly perform the N2 purge operation caused high reticle repairing rates and lots were often scrapped due to precipitation of materials on reticles 201 that were used to process those lots.